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3.3.1.2 Stents:
Stent implantation during lower limb endovascular arterial interventions was initially only reserved as bailout indication in case of complication as a flow limiting dissection or an insufficient intial angiographic result (I.e. residual stenosis >50%) due to an important elastic recoil or an insufficient plaque expansion.
Concerning the iliac arteries, and more specificlly in the common iliac arteries, since many years, primary intention stenting has become the first adopted strategy, because stent implantation at that level is associated with a very high technical success rate as well as a very high longterm patency rate (> 80% at 5 year) (137, 138). Conversely, of what observed in iliacs, the one year restenosis rate at femoral level has remained for many years exceedingly high and this despite an aggressive stenting approach (139, 141).
Balloon expandable, stainless steel stents are no longer used for femoropopliteal disease, because they have significant reocclusion and restenosis rates and do not appear to improve
outcomes after intervention (144-148). Because, the composition of the stent may influence the rate of stent patency after femoropopliteal intervention, a lot of efforts were made from the industry to find the best stent composition to best adapt in this very specific femoropopliteal region.
It is only since 2002, that some improvements were made concerning the SFA stenting
outcomes. Accordingly, the SIROCCO I-II studies (149, 150) were aimed to compare the efficacy and safety of new drug eluting stent (DES) dedicated for SFA lesions. The studies have randomized this new DES to a new nitinol bare metal stent (BMS). The restenosis rate at two years, was for the first time acceptable (i.e. up to 25%), but with surprise comparable between the two studied stents (DES = BMS in term of restenosis). The dissappointement concerning this DES “failure” was considerable, however, this new design nitinol BMS was embrassed with enthusiasm. This new combination of Nickel and Titanium = Nitinol has then become the reference for the conception of new stent design, leading to the performance of several randomized trials aimed to demonstrate the supriority of these new Nitinol BMS compared to standard balloon angioplasty. It is finally in 2006, that in the ABSOLUTE trial the stenting approach proved its superiority to PTA also in SFA lesions, and this especially in case of long and complex lesions (139, 151).
Several hypotheses were made concerning this first generation DES “failure”. The excessive distance between stent’s struts, especially if compared to that one present in coronary DES, has
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probably led to a too weak and inhomogenous antiproliferative medication delivery. Furthermore, the too rapid drug delivery secondary to an inappropriate polymer-drug association was possibly also one reason of an insufficient antiproliferative effect.
Recently, two studies have again tried to reduce SFA restenosis with the use of a second generartion DES. The first one (STRIDES study : long-release polymer everolimus eluting stent:
Abbott Vascular [ClinicalTrials.gov Identifier : NCT00475566], was again not able to significantly reduce the restenosis rate (152), while the second one (ZILVER PTX study : polymerfree paclitaxel eluting stent: Cook Medical [ClinicalTrials.gov Identifier : NCT00120406]) was this time very convincing in term of restenosis rate reduction (153). Accordingly, the ZILVER PTX trial has shown that the DES was superior to the similar version of the BMS in terms of primary patency, and this in all studied sub-group analysis. Despite the fact that the longterm follow-up of the ZILVER PTX study is so far not available, this very promising stent is already regularly used in many catheterization
laboratories in Europe.
3.3.1.3 Drug coated balloons or drug eluting balloons:
After beeing studies first for coronary lesions (154), the drug eluting balloon (DEB) has also made its apperance in the peripheral interventions domains. The hypothesis that by administrating for a relatively short period (1-2 minutes) a high concentration of antiproliferative drug, especially
paclitaxel, at the vessel wall during the balloon inflation has proved its safety and efficacy in two randomized clinical trials.
The THUNDER trial randomly assigned 154 patients with femoropopliteal stenoses to treatment with paclitaxel coated angioplasty balloons, uncoated balloons with paclitaxel dissolved in the contrast medium, or uncoated balloons with contrast solution containing no paclitaxel (155). The primary end point of mean late lumen loss after six months was significantly lower in the coated balloon group than either the paclitaxel solution or control groups (0.4 versus 2.2 and 1.7 mm, respectively). The coated balloon group also had a significantly lower rate of target lesion revascularization at six months (4 versus 29 and 37%). These positive results were maintained at two years.
The findings of the THUNDER trial were confirmed in the similarly designed FemPac trial and the non-yet published LEVANT-1 trial. Accordingly, in the FemPac trial 87 patients undergoing
angioplasty of femoropopliteal lesions were randomly assigned to either uncoated or paclitaxel-coated
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balloons catheters (156). The primary end point of late lumen loss at six month follow-up angiography was significantly less in the coated balloon group (0.5 versus 1.0 mm).
So far, a lot of enthusiasm is associated with this DEB technology, because it combines an easy to use technology (i.e. balloon angioplasty) with an efficacious way to prevent restenosis (i.e.
antiproliferative local drug delivery). The fact that after having delivered the drug no foreign body (e.g.
stent) remains in the vessel is particularly attractive especially when dealing with SFA lesion, where stent fractures may be observed (157). Presently several larger randomized trials, including patients presenting with SFA lesions, as well as patients presenting with criticial limb ischemia secondary to below the knee lesions are underway (158), and very soon more data supporting this very promising technology will be at our disposal, in order to widespread this DEB technology to more patients and more lesions’ subsets.
3.3.2 Endovascular Revascularization Outcomes
In order to better categorize outcome data, the following terminology is used (159):
A graft or a stent is considered to have primary patency if there has been uninterrupted patency without a procedure being necessary or performed to deal with disease progression in the adjacent native vessel, such as transluminal dilatation or proximal or distal extension to the graft (159).
The term primary assisted patency is used when a graft or a stent is developing a restenosis or an incipient re-occlusion, but patency, even in the absence of symptoms has been restored with an endovascular (e.g. PTA or stenting) or a surgical (e.g. anastomosis revision)
intervention.
The term secondary patency is used if the graft or the stent has become occluded but patency has been restored with thrombectomy, thrombolysis, or transluminal angioplasty, or if there are problems with the graft itself or one of its anastomoses that requires revision or
reconstruction.
Table 4 shows the 2-5 years patency rates observed after different types of revascularization procedures - endovascular (angioplasty vs. stent) as well as the patency rates observed according to the level of revascularization procedure – iliac, femoro-popliteal, infra-popliteal. Finally, Table 4
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suggests that according to the initial clinical scenario (e .g. claudication vs. CLI), as well as according to the complexity (stenosis vs. occlusion) and the localization of the treated lesion (in-flow vs. out-flow vs. below the knee), the awaited patency rates are reduced, and this independently of which type of revascularization procedure is performed (2).